Method and apparatus to use auxiliary receiver to compensate multiple transmitters based upon one of the transmitters

ABSTRACT

A communications device includes a plurality of wireless transmitters operable at different respective frequencies and each configured to generate respective IQ signals having an initial IQ imbalance. An auxiliary receiver is coupled to a given wireless transmitter. In addition, a controller is configured to apply predistortion to the each wireless transmitter of the plurality thereof based upon the initial IQ imbalance generated by the given wireless transmitter to reduce the initial IQ imbalance in each wireless transmitter.

TECHNICAL FIELD

The present disclosure relates to the field of communications devices,and more particularly, communications devices with components thatcorrect initial IQ imbalances.

BACKGROUND

In general, undesired or non-ideal characteristics, such as DC offsetand in-phase/quadrature-phase (IQ) imbalance, degrade performance ofmobile transceivers. The DC offset is the effect of self mixing by amixer, and occurs when a signal of a local oscillator (LO) returns afterleaking toward an antenna or when a radio frequency (RF) modulationsignal input through the antenna is leaked to the local oscillator.Another way to create DC offset is through an inherent offset in theamplifiers due to imbalances. If the DC offset is amplified byamplifiers in the signal path, then this way may saturate a basebandcircuit.

The IQ imbalance is caused when the phase difference between thein-phase (I) channel signal and the quadrature-phase (Q) channel signalgenerated in an oscillator of a wireless transmitter is not 90 degrees.The IQ imbalance can be reduced by designing mixers of the I channeldemodulator and the Q channel demodulator to be precisely 90 degrees inphase delay (i.e., orthogonal) to each other. However, designing themixers so that there is precisely a 90 degrees phase difference to eachother is not practical over process and temperature variations. This isbecause in the layout, the I and Q paths to the mixers traversedifferent lengths despite the best effort of keeping everythingsymmetrical. This is especially true for multi-band systems. An IQimbalance increases the Bit Error Rate (BER), thereby degrading theperformance of the wireless transceiver.

However, there is still a need to improve such compensation, and a needto reduce IQ imbalances and the associated distortion in mobiletransmitters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a first embodiment of acommunications device the present disclosure.

FIG. 2 is a schematic block diagram of a second embodiment of acommunications device of the present disclosure.

FIG. 3 is a schematic block diagram illustrating components of a mobilewireless communications device in accordance with an example embodimentof the present disclosure.

DETAILED DESCRIPTION

The present description is made with reference to the accompanyingdrawings, in which various embodiments are shown. However, manydifferent embodiments may be used, and thus the description should notbe construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete. Like numbers refer to like elements throughout, and primenotation is used to indicate similar elements or steps in alternativeembodiments.

Generally speaking, a communications device may include a plurality ofwireless transmitters operable at different respective frequencies andeach configured to generate respective IQ signals having an initial IQimbalance. An auxiliary receiver may be coupled to a given wirelesstransmitter. A controller may be configured to apply predistortion tothe each wireless transmitter of the plurality thereof based upon theinitial IQ imbalance generated by the given wireless transmitter toreduce the initial IQ imbalance in each wireless transmitter.

Each wireless transmitter may comprise a digital signal processing (DSP)block configured to receive an input baseband signal and to generate theIQ signal having the IQ imbalance, and the controller may be configuredto apply predistortion by generating and applying a predistortion signalto the DSP block. In addition, each wireless transmitter may furthercomprise at least one digital to analog converter (DAC) coupleddownstream of the DSP block.

At least one mixer may be coupled downstream of the at least one DAC. Aphase locked loop (PLL) may be coupled to the at least one mixer. Atleast one power amplifier may be downstream from the at least one mixer.

The auxiliary receiver may have a low noise amplifier (LNA), and atleast one mixer coupled downstream of the LNA. A receiver phase lockedloop (RXPLL) may be coupled to the at least one mixer. At least oneanalog to digital converter (ADC) may be coupled downstream of the atleast one mixer, and a receiver DSP block may be coupled to the at leastone ADC.

A method aspect is directed to a method of operating a communicationsdevice comprising a plurality of wireless transmitters operable atdifferent respective frequencies and each configured to generaterespective IQ signals having an initial IQ imbalance, an auxiliaryreceiver coupled to a given wireless transmitter, and a controller. Themethod may include applying predistortion to the each wirelesstransmitter of the plurality thereof based upon the initial IQ imbalancegenerated by the given wireless transmitter to reduce the initial IQimbalance in each wireless transmitter, using the controller.

With reference to FIG. 1, a communications device 20 is now described.The communications device 20 may be a mobile wireless communicationsdevice, such as a smartphone. The communications device 20 may be amulti-frequency band device that operates over a 2.4 GHz frequency band(i.e., approximately 2.4 to 2.483 GHz) and over a 5 GHz frequency band(i.e., approximately 4.9 to 6 GHz), for example. Depending on theintended application, the communications device 20 may operate overother frequency bands, as readily appreciated by those skilled in theart.

The communications device 20 includes a plurality of transmitters 22,42, and a tunable auxiliary receiver 62. The communications device mayinclude a housing commonly carrying the transmitters 22, 42 and thetunable auxiliary receiver. As will be explained in detail below, acontroller 21 uses the tunable auxiliary receiver 62 to detectimpairments such as initial IQ imbalances in signals output by thetransmitters 22, 42 and directs the digital signal processing (DSP)blocks 24, 44 of the transmitters to correct input baseband signals soas to reduce the IQ imbalance in the signals output by the transmitters.The tunable auxiliary receiver 62 is coupled to one of the transmitters24, 44 at a time by the switching block 80, and is tunable to receivedifferent frequencies so as to be able to service different transmittersoperating at different frequencies.

The transmitter 22 will now be described in details. The transmitter 22includes a transmit (TX) DSP block 24 configured to output basebandsignal having in-phase (I) and quadrature (Q) components and totherefore generate and output complex IQ signals. The complex IQ signalshave an IQ imbalance caused by other components of the transmitter 22,meaning that there may be a phase imbalance between the I and Q signals(e.g. I and Q are not 90° apart in phase). The TX DSP block 24 comprisesa data modulator 25 that generates the baseband signal, and a transmitcompensator (TX compensator) 27 coupled thereto. As will be explainedbelow, the controller 21 corrects the initial IQ imbalance using the TXcompensator 27.

The I and Q outputs from the TX DSP block 24 are mixed by the mixers 28a, 28 b to a low intermediate frequency (IF) by a low IF source 26coupled to the mixers. Digital to analog converters (DACs) 30 a, 30 bare coupled to the mixers 28 a, 28 b, and low pass filters 32 a, 32 bare coupled to the DACs.

Mixers 36 a, 36 b are coupled to the low pass filters 32 a, 32 b. Thecomplex IQ signals are driven to the desired transmit frequency by thetransmitter phase locked loop 34, which is coupled to the mixers 36 a,36 b. The complex IQ signals (now at the desired transmit frequency) aresummed by the summer 37, and then fed downstream to a pre-poweramplifier 38, and in turn to a power amplifier 40. The power amplifier40 outputs a RF modulated signal having the initial IQ imbalance. Thepre-power amplifier 38 is used to ensure that there is enough power todrive the power amplifier 40.

The transmitter 42 contains similar components to the transmitter 22 andneeds no further discussion herein, although it should be understoodthat the transmitter 42 may operate in a different frequency band thanthe transmitter 22. In addition, it should be understood that thecommunications device 20 may include any numbers of transmitters, andthat they make be similar to the transmitters 22, 42, or may bedifferent kinds of transmitters. The transmitters 22, 42 are eachcoupled to the switching block 80, which is in turn coupled to thefrequency tunable auxiliary receiver 62.

An RF modulated signal having the initial IQ imbalance from atransmitter 22, 42 is provided to the frequency tunable auxiliaryreceiver 62 using a non-directional coupler 82, 86 coupled between thepre-power amplifier 38, 58 and the power amplifier 40, 60.Alternatively, a non-directional coupler 84, 88 may be coupled betweenthe power amplifier 40, 60 and the antenna (not shown).

An advantage of using a non-directional coupler 82, 86 is that it canoperate over a wide band of operation, and its performance remains wellcontrolled over temperature and frequency changes. In addition, anon-directional coupler 82, 86 helps to prevent the PLL 74 of thefrequency tunable auxiliary receiver 62 from parasitically coupling tothe output of the transmitter 16. Instead of using a non-directionalcoupler, it is possible to use a directional coupler. The use of adirectional coupler provides a steady feedback signal independent of theVSWR variation at the antenna or the PPA load. However, anon-directional coupler is preferred because it is wideband and simplerto implement.

The switching block 80 couples one of the transmitters 22, 42 at a timeto the frequency tunable auxiliary receiver 62 via the couplers 82, 86,84, 88. The frequency tunable auxiliary receiver 62 is used to servicethe needs of the transmitters 22, 42. Estimation and compensation for IQimbalance and DC offset are examples of servicing the needs of thetransmitters 22, 42, as will be appreciated by those skilled in the art.

The frequency tunable auxiliary receiver 62 can be of lower performanceas compared to a main receiver (not shown) of the communications device20 since it is primarily designed to serve the transmitters 22, 42. Forexample, the frequency tunable auxiliary receiver 62 may not need tohave a high dynamic range like a main receiver, nor a high selectivity.

The frequency tunable auxiliary receiver 62 is configured to have anindependent, dedicated phase-locked loop 74 that is offset from the TXPLL 34, 54 operating the transmitters 22, 42. This advantageously allowsthe initial IQ imbalance, to be separated in the frequency domain fromIQ imbalances or other impairments added in the frequency tunableauxiliary receiver 62.

As explained above, the auxiliary receiver 62 includes a low noiseamplifier 78 to receive the RF modulated signal having the IQ imbalance.The output of the low noise amplifier 78 is provided to the mixers 76 a,76 b. The frequency tunable auxiliary receiver 62 is configured as aO-IF receiver since the transmitters 22, 42 are is configured as low-IFtransmitters (i.e., dual-mixer mode). This means that a second set ofmixers 68 a, 68 b may not be needed and is selectively set to a value of1 (i.e., e^(j0)) by the low IF source 66. In a different embodiment, theswitching block 80 can be combined with the LNA 78 to provide two inputpairs, one of which is selected under software control.

The mixers 76 a, 76 b receive the RF modulated signal having the IQimbalance, and I and Q local oscillator signals from the RX PLL 74. Asnoted above, the frequency tunable auxiliary receiver 62 is configuredto have an independent, dedicated phase-locked loop 74 that is offsetfrom the PLL's 34, 54 of the transmitters 22, 42. This advantageouslyallows the initial IQ imbalance in the RF modulated signal to beseparated in the frequency domain from impairments added in thefrequency tunable auxiliary receiver 62.

The output of the mixers 76 a, 76 b provide receive modulated analog Iand Q component signals at the intermediate frequency. These signals areprovided to low pass filters 72 a, 72 b and then to analog-to-digitalconverters 70 a, 70 b so that the receive baseband modulated analog Iand Q component signals are now receive baseband modulated digital I andQ component signals at the intermediate frequency. The receive basebandmodulated digital I and Q component signals at the intermediatefrequency include the receive impairment (initial IQ imbalance)spectrally separated from the transmit impairment. These signals arepassed through the mixers 68 a, 68 b, which translate this complexsignal to zero-IF in a second down-conversion operation by frequencyusing the low IF source 46.

The controller 21 is coupled to the output of the data modulator 25, 45and to the output of the frequency tunable auxiliary receiver 62. Thecontroller 21 receives the transmit baseband modulated signal from thedata modulator 25, 45. The transmit baseband modulated signal is alsoreferred to as the reference signal since it does not include theinitial IQ imbalance from the transmitters 22, 42.

The controller 21 also receives the receive baseband modulated signal asprovided by the auxiliary receiver 62. The receive baseband modulatedsignal includes the transmit baseband modulated signal as well as thereceive impairment spectrally separated from the transmit impairment.

The controller 21 includes a delay circuit 90 configured to delay thetransmit baseband modulated signal so that this signal and the receivebaseband modulated signal match up in time when compared. The delaycircuit 90 may be configured to implement a fixed delay corresponding toinherent delays of the transmitters 22, 42 and the auxiliary receiver62, and a variable delay corresponding to variable environmentalconditions. The variable delay accounts for environmental conditions,such as operating temperature variations, for example. In particular,the analog sections within the transmitter 22, 42 and the auxiliaryreceiver 62 are affected by temperature variations.

The impairment module 92 within the controller 21 estimates the IQimbalance and other impairment within the selected transmitter 22, 42,and generates an IQ or impairment compensation signal for thattransmitter based on the estimated transmit impairment.

As stated above, the transmitters 22, 42 include transmit impairmentcompensators 27, 47 configured to compensate the transmit basebandmodulated signal based on the compensation signal. The transmitimpairment compensators 27, 47 are positioned between the datamodulators 25, 45 and the mixers 28 a, 28 b, 48 a, 48 b. Alternatively,the transmit impairment compensator 27 may be implemented within thecontroller itself if the transmitter chain is routed through thecontroller 21.

The impairment module 92 is configured to estimate the transmitimpairment by comparing the transmit baseband modulated signal with thereceive baseband modulated signal while ignoring the receive impairment.The impairment module 92 performs the comparing in a plurality ofiterations to determine difference values therebetween. The transmitimpairment compensators 27, 47 then perform the compensation byiteratively adding correction values, as provided by the compensationsignal, to the transmit baseband modulated signal to compensate for thedifference values from the plurality of iterations. A least means square(LMS) algorithm may be used to determine the compensation values, forexample.

Operation of the impairment module 92 may be simplified based onadditional filtering of the receive baseband modulated signal beforebeing provided as an input to the impairment module 92. In the aboveembodiment, the controller 21 typically includes a filter 94 that shouldhelpfully be large enough to pass the transmit impairment portion of thesignal while rejecting the receive impairment portion of the signal.After the second down-conversion in the auxiliary receiver 21, thetransmit impairment signal centers at DC and can be isolated from thereceiver impairments using a lowpass filter. This filter 94 isolates thetransmit impairment signal so that the controller 21 can compare it tothe ideal reference signal and estimate the impairments using the LMSalgorithm or a different method.

In another embodiment of this filter 94, a complex filter may be used.The complex filter is used to select the positive frequencies, which arethen provided to the impairment module 94 after translating the positivefrequencies at zero-IF.

As an alternative to the complex filter, a lossy integrator may filterthe zero-IF down-converted signal in the auxiliary receiver 62. Thisfilter can be implemented very simply to have a cascade of filters, eachwith a single-pole IIR response. This filter implementation isinexpensive, yet very powerful. The filtering operation modifies thein-band frequency components of the auxiliary receiver output signal.Hence, it may be compared to a similarly modified reference signal(i.e., the ideal transmit signal from the data modulators 25, 45). Thesame LMS update equations can be used to estimate the impairments causedin the transmitter.

The impairment module 94 may also be used to estimate and generate areceive impairment compensation signal to correct for impairments withinthe auxiliary receiver 62. The auxiliary receiver 62 includes a receiveimpairment compensation signal for the receive impairment compensator orDSP block 64 within the auxiliary receiver 62.

The receive impairment compensator 64 is at the output of the mixers 68a, 68 b. Alternatively, the receive impairment compensator 64 may beimplemented within the controller itself if the receive chain is routedthrough the controller 21. As discussed above for the estimation andcompensation of the transmit impairment, an inverse system modeling isalso used for the receive impairment

As discussed above, complex filtering and very selective complex lossyintegrator filtering may be used to provide inputs to the impairmentmodule 92. In addition, the receive impairment may be estimated withoutrequiring the transmit baseband modulated signal. Instead, a veryselective complex lossy integrator may be used to extract a portion ofthe signal spectrum centered at the positive intermediate frequency, anda very selective complex lossy integrator may be used to extract aportion of the signal spectrum centered at the negative intermediatefrequency.

With reference to FIG. 2, an additional embodiment is now described.Here, the transmitters 22′, 42′, controller 21′, and auxiliary receiver62′ are similar to those described above, and are all integrated in asingle integrated circuit. However, in this embodiment, there is noswitching block, and the auxiliary receiver is coupled to the output ofonly one of the transmitters 22′.

Since multiple transmitters implemented in a same integrated circuit aresubject to approximately the same temperature, the performance of eachtransmitter is affected similarly due to heat. Therefore, in someapplications, the impairment correction applied by the impairment module92′ and TX compensator 27′ to correct the initial IQ imbalance in thetransmitter 22′, can be applied to the second transmitter 42′ to obtainsimilar results. This reduces the cost of the communications device 20′because less processing power may be used. As such, in this embodiment,the impairment correction applied by the impairment module 92′ and TXcompensator 47′ to the transmitter 42′ is the same as, or based upon,the impairment correction applied to the transmitter 22′ (based upon thedetected IQ imbalance in the transmit signal output by the transmitter42′).

Further details of the auxiliary receiver 62, 62′ may be found inco-pending application “WIRELESS COMMUNICATIONS DEVICE WITH IMPAIRMENTCOMPENSATION AND ASSOCIATED METHODS,” Attorney Docket Number39393-US-PAT (85311), assigned to the same assignee as the presentapplication, the contents of which are hereby incorporated by referencein their entirety.

Example components of a hand-held mobile wireless communications device1000 that may be used in accordance with the present disclosure arefurther described in the example below with reference to FIG. 3. Thedevice 1000 illustratively includes a housing 1200, a keypad 1400 and anoutput device 1600. The output device shown is a display 1600, which maycomprise a full graphic LCD. In some example embodiments, display 1600may comprise a touch-sensitive input and output device. Other types ofoutput devices may alternatively be utilized. A processing device 1800is contained within the housing 1200 and is coupled between the keypad1400 and the display 1600. The processing device 1800 controls theoperation of the display 1600, as well as the overall operation of themobile device 1000, in response to actuation of keys on the keypad 1400by the user. In some example embodiments, keypad 1400 may comprise aphysical keypad or a virtual keypad (e.g., using a touch-sensitiveinterface) or both.

The housing 1200 may be elongated vertically, or may take on other sizesand shapes (including clamshell housing structures). The keypad 1400 mayinclude a mode selection key, or other hardware or software forswitching between text entry and telephony entry.

In addition to the processing device 1800, other parts of the mobiledevice 1000 are shown schematically in FIG. 3. These include acommunications subsystem 1001; a short-range communications subsystem1020; the keypad 1400 and the display 1600, along with otherinput/output devices 1060, 1080, 1100 and 1120; as well as memorydevices 1160, 1180 and various other device subsystems 1201. The mobiledevice 1000 may comprise a two-way RF communications device having voiceand data communications capabilities. In addition, the mobile device1000 may have the capability to communicate with other computer systemsvia the Internet.

Operating system software executed by the processing device 1800 may bestored in a persistent store, such as the flash memory 1160, but may bestored in other types of memory devices, such as a read only memory(ROM) or similar storage element. In addition, system software, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile store, such as the random access memory (RAM) 1180.Communications signals received by the mobile device may also be storedin the RAM 1180.

The processing device 1800, in addition to its operating systemfunctions, enables execution of software applications 1300A-1300N on thedevice 1000. A predetermined set of applications that control basicdevice operations, such as data and voice communications 1300A and1300B, may be installed on the device 1000 during manufacture. Inaddition, a personal information manager (PIM) application may beinstalled during manufacture. The PIM may be capable of organizing andmanaging data items, such as e-mail, calendar events, voice mails,appointments, and task items. The PIM application may also be capable ofsending and receiving data items via a wireless network 1401. The PIMdata items may be seamlessly integrated, synchronized and updated viathe wireless network 1401 with the device user's corresponding dataitems stored or associated with a host computer system.

Communication functions, including data and voice communications, areperformed through the communications subsystem 1001, and possiblythrough the short-range communications subsystem. The communicationssubsystem 1001 includes a receiver 1500, a transmitter 1520, and one ormore antennas 1540 and 1560. In addition, the communications subsystem1001 also includes a processing module, such as a digital signalprocessor (DSP) 1580, and local oscillators (LOs) 1601. The specificdesign and implementation of the communications subsystem 1001 isdependent upon the communications network in which the mobile device1000 is intended to operate. For example, a mobile device 1000 mayinclude a communications subsystem 1001 designed to operate with theMobitex™, Data TACT or General Packet Radio Service (GPRS) mobile datacommunications networks, and also designed to operate with any of avariety of voice communications networks, such as AMPS, TDMA, CDMA,WCDMA, PCS, GSM, EDGE, etc. Other types of data and voice networks, bothseparate and integrated, may also be utilized with the mobile device1000. The mobile device 1000 may also be compliant with othercommunications standards such as 3GSM, 3G, UMTS, 4G, etc.

Network access requirements vary depending upon the type ofcommunication system. For example, in the Mobitex and DataTAC networks,mobile devices are registered on the network using a unique personalidentification number or PIN associated with each device. In GPRSnetworks, however, network access is associated with a subscriber oruser of a device. A GPRS device therefore utilizes a subscriber identitymodule, commonly referred to as a SIM card, in order to operate on aGPRS network.

When required network registration or activation procedures have beencompleted, the mobile device 1000 may send and receive communicationssignals over the communication network 1401. Signals received from thecommunications network 1401 by the antenna 1540 are routed to thereceiver 1500, which provides for signal amplification, frequency downconversion, filtering, channel selection, etc., and may also provideanalog to digital conversion. Analog-to-digital conversion of thereceived signal allows the DSP 1580 to perform more complexcommunications functions, such as demodulation and decoding. In asimilar manner, signals to be transmitted to the network 1401 areprocessed (e.g. modulated and encoded) by the DSP 1580 and are thenprovided to the transmitter 1520 for digital to analog conversion,frequency up conversion, filtering, amplification and transmission tothe communication network 1401 (or networks) via the antenna 1560.

In addition to processing communications signals, the DSP 1580 providesfor control of the receiver 1500 and the transmitter 1520. For example,gains applied to communications signals in the receiver 1500 andtransmitter 1520 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 1580.

In a data communications mode, a received signal, such as a text messageor web page download, is processed by the communications subsystem 1001and is input to the processing device 1800. The received signal is thenfurther processed by the processing device 1800 for an output to thedisplay 1600, or alternatively to some other auxiliary I/O device 1060.A device user may also compose data items, such as e-mail messages,using the keypad 1400 and/or some other auxiliary I/O device 1060, suchas a touchpad, a rocker switch, a thumb-wheel, track ball, or some othertype of input device. The composed data items may then be transmittedover the communications network 1401 via the communications subsystem1001.

In a voice communications mode, overall operation of the device issubstantially similar to the data communications mode, except thatreceived signals are output to a speaker 1100, and signals fortransmission are generated by a microphone 1120. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the device 1000. In addition, the display 1600may also be utilized in voice communications mode, for example todisplay the identity of a calling party, the duration of a voice call,or other voice call related information.

The short-range communications subsystem enables communication betweenthe mobile device 1000 and other proximate systems or devices, whichneed not necessarily be similar devices. For example, the short-rangecommunications subsystem may include an infrared device and associatedcircuits and components, or a Bluetooth™ communications module toprovide for communication with similarly-enabled systems and devices.Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. A communications device comprising: aplurality of wireless transmitters operable at different respectivefrequencies and each configured to generate respective IQ signals havingan initial IQ imbalance; an auxiliary receiver coupled to a givenwireless transmitter; and a controller configured to apply predistortionto the each wireless transmitter of the plurality thereof based upon theinitial IQ imbalance generated by the given wireless transmitter toreduce the initial IQ imbalance in each wireless transmitter.
 2. Thecommunications device of claim 1, wherein each wireless transmittercomprises a digital signal processing (DSP) block configured to receivean input baseband signal and to generate the IQ signal having the IQimbalance; and wherein said controller is configured to applypredistortion by generating and applying a predistortion signal to saidDSP block.
 3. The communications device of claim 2, wherein eachwireless transmitter further comprises at least one digital to analogconverter (DAC) coupled downstream of said DSP block.
 4. Thecommunications device of claim 3, wherein each wireless transmitterfurther comprises at least one mixer coupled downstream of said at leastone DAC.
 5. The communications device of claim 4, wherein each wirelesstransmitter further comprises a phase locked loop (PLL) coupled to saidat least one mixer.
 6. The communications device of claim 5, whereineach wireless transmitter further comprises at least one power amplifierdownstream from said at least one mixer.
 7. The communications device ofclaim 1, wherein said auxiliary receiver comprises a low noise amplifier(LNA), and at least one mixer coupled downstream of said LNA.
 8. Thecommunications device of claim 7, wherein said auxiliary receiverfurther comprises a receiver phase locked loop (RXPLL) coupled to saidat least one mixer.
 9. The communications device of claim 8, whereinsaid auxiliary receiver further comprises at least one analog to digitalconverter (ADC) coupled downstream of said at least one mixer, and areceiver DSP block coupled to said at least one ADC.
 10. Acommunications device comprising: a portable housing; a plurality ofwireless transmitters operable at different respective frequencies andeach configured to generate respective IQ signals having an initial IQimbalance, said plurality of wireless transmitters carried by saidportable housing; each wireless transmitter comprising a digital signalprocessing (DSP) block configured to receive an input baseband signaland to generate the IQ signal having the IQ imbalance; an auxiliaryreceiver coupled to a given wireless transmitter and carried by saidportable housing; and a controller configured to apply predistortion tothe each wireless transmitter of the plurality thereof based upon theinitial IQ imbalance generated by the given wireless transmitter toreduce the initial IQ imbalance in each wireless transmitter bygenerating and applying a predistortion signal to said DSP block, andcarried by said portable housing.
 11. The communications device of claim10, wherein each wireless transmitter further comprises at least onedigital to analog converter (DAC) coupled downstream of said DSP block.12. The communications device of claim 11, wherein each wirelesstransmitter further comprises at least one mixer coupled downstream ofsaid at least one DAC.
 13. The communications device of claim 12,wherein each wireless transmitter further comprises a phase locked loop(PLL) coupled to said at least one mixer.
 14. The communications deviceof claim 10, wherein said auxiliary receiver comprises a low noiseamplifier (LNA), and at least one mixer coupled downstream of said LNA.15. The communications device of claim 14, wherein said auxiliaryreceiver further comprises a receiver phase locked loop (RXPLL) coupledto said at least one mixer.
 16. A method of operating a communicationsdevice comprising a plurality of wireless transmitters operable atdifferent respective frequencies and each configured to generaterespective IQ signals having an initial IQ imbalance, an auxiliaryreceiver coupled to a given wireless transmitter, and a controller, themethod comprising: applying predistortion to the each wirelesstransmitter of the plurality thereof based upon the initial IQ imbalancegenerated by the given wireless transmitter to reduce the initial IQimbalance in each wireless transmitter, using the controller.
 17. Themethod of claim 16, wherein each wireless transmitter comprises adigital signal processing (DSP) block configured to receive an inputbaseband signal and to generate the IQ signal having the IQ imbalance;wherein the controller is configured to apply predistortion bygenerating and applying a predistortion signal to the DSP block; andwherein each wireless transmitter further comprises at least one digitalto analog converter (DAC) coupled downstream of the DSP block.
 18. Themethod of claim 17, wherein each wireless transmitter further comprisesat least one mixer coupled downstream of the at least one DAC; whereineach wireless transmitter further comprises a phase locked loop (PLL)coupled to the at least one mixer; and wherein each wireless transmitterfurther comprises at least one power amplifier downstream from the atleast one mixer.
 19. The method of claim 16, wherein the auxiliaryreceiver comprises a low noise amplifier (LNA), and at least one mixercoupled downstream of the LNA; and wherein the auxiliary receiverfurther comprises a receiver phase locked loop (RXPLL) coupled to the atleast one mixer.
 20. The method of claim 19, wherein the auxiliaryreceiver further comprises at least one analog to digital converter(ADC) coupled downstream of the at least one mixer, and a receiver DSPblock coupled to the at least one ADC.